It has been well known that fescue grass containing
the endophytic fungus, Acremonium coenophialum, has detrimental effects
on pregnant mares
when consumed during late gestation. Common problems
include prolonged gestation, dystocia (foaling problems), agalactia (no
milk production)
thickened placenta, poor foal viability and decreased
concentrations of
prolactin and progesterone. However, few studies have
evaluated the effects
of this fungus on early pregnancy. Dr.J.P. Brendemuehl,
at Tuskegee
University in Alabama, has done some work with respect
to the effects
of infected fescue on the transitional mare.
During spring transition, the
number and size of follicles from January through
April were found to be
lower and smaller in mares grazing on endophyte-infected
fescue pastures compared to mares on non-endophyte pastures. The time to
first ovulation
was also delayed 43 days in mares ingesting infected
fescue (May 28 vs.
April 15). Brendemuehl and coworkers also found
that cycling mares were affected by endophyte-ridden fescue. Prolonged
luteal function, decreased pregnancy rates on a per cycle basis and increased
embryonic death rates
were all evident in cycling mares that grazed on infected
fescue. Forty-five
percent (45 %) of the mares on infected pastures were
pregnant 14 days
after ovulation compared to 75 % of mares that grazed
on endophyte-free
fescue. Also noted 30 % of those mares ingesting
the endophyte-ridden
fescue lost their pregnancies during early embryonic
development compared
to 10 % of the mares on endophyte-free pastures. From
these data, it
appears evident that endophyte-ridden fescue can have
dramatic effects
on the transitional and cycling mare.
The objective of a recent
study by Arns and coworkers (1997) was to
investigate the effects of increasing dietary concentrations
of ergovaline,
the problematic ergot alkaloid produced by A.coenophialum,
on
establishment and maintenance of pregnancy in the
mare. Earlier work
by Brendemuehl, (1994) examined the reproductive status
of bred mares ingesting 1171 Ng ergovaline/g wet grass. Therefore, Arns
and associates
felt it necessary to evaluate the effects of lower
levels of ergovaline
consumption. Twelve cycling mares of light-horse breeds
were randomly
assigned to receive diets that contained either no
ergovaline, low levels
(150158 ppb ergovaline/kg total diet) of ergovaline
or high levels
(308315 ppb ergovaline/kg total diet) of ergovaline.
The diet of each mare consisted of 52 % orchard grass and 48 % grain concentrate.
Dietary
ergovaline was introduced as infected fescue seed
mixed into the
concentrate. Following 7 days of diet acclimation,
reproductive cycles of
all mares were monitored for follicular development
and ovulation. Mares
in estrus were bred every other day by artificial
insemination once a follicle
reached 30 mm in size. In evaluating body condition
score, those mares fed
the high ergovaline (HE) diet tended to have a lower
average daily weight
gain compared to those mares fed no ergovaline (NE).
Mares on low
ergovaline (LE) diets had cycles per conception, length
of estrus and
preovulatory size of follicles. All of these parameters
were found to be
similar for mares in all three groups. Consumption
of infected fescue seed
also did not have an effect on embryonic vesicular
sizes on day 14, 21 or 28
of gestation. There were however, higherprogesterone
concentrations during
the luteal phase in mares fed LE or HE diets. Also,
prolactin concentrations
were lower in LE and HE mares. The researchers of
this study believe that
weight los occurred as a result of a decrease in food
consumption rather than
a direct effect from injecting ergot alkaloids. Also,
small sample size and individual variation may have been responsible for
the lower progesterone concentrations found in mares fed no ergovaline.
Brendemuchl (1994) as
well as studies in other species clearly defined endophyte-fed
animals as
having lower progesterone levels.
Few studies have accurately quantified
the amount of toxin (ergot alkaloid) necessary to induce an effect on nutritional
or reproductive status in horses.
It is clear that infected fescue pastures elicit different
effects in gestating
mares from year to year. Concentrations of ergot alkaloids
do fluctuate with management and environmental conditions. Work by Arns
seems to suggest
that dietary concentrations of ergovaline up to 308
ppb/kg total diet
consumed has no adverse effects on reproductive performance
in cycling
mares. Signs of fescue toxicosis have been seen in
horses fed concentrations
of ergovaline in excess of 325 ppb/kg total diet.
More research is needed
before one can recommend a specific concentration
of ergot alkaloid that is
safe.
It may be
prudent for any horse breeder living in a region of the country where fescue
grass is prominent to assess their pastures for endophyte infestation.
Virginia pastures are well known for their prominence of tall
fescue grass. Testing of pastures at ERC found that
fescue grass made
up 20-30% of the total grass population in the fields
and 58 % of the fescue
was indeed infested with the endophyte fungus. Because
consumption of
certain levels of endophyte-ridden fescue has been
shown to affect mares
during the first 30 days and last 30 days of gestation,
one should constantly
be aware of exposure in pasture as well as in
cut hay being fed. Apparently,
ingestion of infected fescue has little to no affect
on mares in the middle of gestation. The present policy at Equine Reproduction
Concepts is that no
mare at our facility will be exposed endophyte-ridden
fescue in cut hay or
pasture form, during breeding, early gestation (first
60 days) or late
gestation (last 45-60 days). If someone is concerned
that their pregnant
mare has been exposed to infected fescue during a
vulnerable period,
please consult a veterinarian for possible treatment.